This invention relates to carriers for wafers that are processed into semiconductor units, including enclosures for holding wafers in a horizontal orientation.
Semiconductor wafers are subjected to numerous steps during processing in various pieces of processing equipment. The wafers must be transported from workstation to workstation and often must be temporarily stored in order to accommodate the necessary processing steps. Moreover, the wafers must sometimes be transported or shipped from a wafer manufacturing facility to another site where they are further processed. A number of types of transport and shipping devices have been previously known for handling, storing and shipping wafers. A “coin stack” wafer carrier is a type of shipper that holds the wafers in a horizontal position for transport.
The semiconductor industry is currently moving toward processing larger and larger wafers into semiconductors. As semiconductors have become larger in scale, that is, as the number of circuits per unit area has increased, contaminants in the form of particulates have become more of an issue. The size of particulates that can destroy a circuit has decreased and is approaching the molecular level.
Contaminants besides particulates should also be controlled. Chemical species that coat the wafers can interfere with subsequent processing steps. Charged ions and amines are especially undesirable contaminants. Contaminant and particulate control are necessary during all phases of manufacturing, processing, transporting, and storage of semiconductor wafers.
Wafers must be protected from damage during shipping. The carrier system must protect wafers from breakage and from shocks, for example, as when dropped. An important component of such protection is a wafer cushion on the bottom of the interior of the wafer carrier. The wafer cushion must protect the wafers from breakage but must not contaminate them with particulates and/or chemical species.
Conventional materials used in foam wafer cushions are treated to have static-control properties, including anti-static, static-dissipative, and conductive properties. The wafer cushions are typically manufactured by creating a bulk foam material that is subsequently processed into individual foam cushions. Conventional materials undergo another processing step to endow them with static control properties. Typical treatments involve impregnating the foam material with carbon and/or treating its surface with chemicals.
The semiconductor industry conventionally uses polyurethanes or open-cell polyethylene foams for wafer cushions. These materials are favored because they have good engineering properties and provide generally adequate protection from damage. These cushions, however, outgas ions, amines, and other chemical species that contaminate the wafers. The semiconductor industry needs wafer carriers that provide adequate damage protection and particulate protection without contaminating the wafers in the shipper.